1. Field of the Invention
The present invention relates to a printer with a head that is recordable a plurality of different inks on a printing medium, as well as to a corresponding method of printing, an ink cartridge used for such a printer, and a program product utilized by such a printer.
2. Description of the Related Art
Color printers with a head that records a plurality of different color inks on a printing medium are widely used as an output device of a computer, which prints an image processed by the computer in a multi-color, multi-tone manner. There are a variety of known methods to record ink on the printing medium: a thermal transfer mechanism that fuses ink on an ink ribbon and transfers the fused ink to printing paper; an ink jet mechanism that ejects color ink drops onto printing paper; and an electrophotographic mechanism that generates a latent image on a photosensitive material by means of laser and transfers one or plural color toners corresponding to the generated latent image. In any of such mechanisms, a plurality of different color inks are mixed to reproduce colors in a predetermined range of hues. Three primary color inks, cyan (C), magenta (M), and yellow (Y) are typically used for full-color printing. A black ink is provided in addition to these three primary color inks CMY, in order to ensure high-speed printing of letters (generally in black) and reduce the total quantity of inks used for printing by the under color removal.
A variety of techniques, such as the dither method and the error diffusion method may be applied to print a multi-color, multi-tone image with a plurality of different inks. In any of these applicable techniques, the printer carries out printing with dots of a specific size corresponding to a preset printing resolution. The printers generally have the printing density or printing resolution in the range of 300 dpi to 720 dpi and the particle diameter of several tens microns. Even the newly developed high-resolution printers have the printing resolution of about 1440 dpi. This is, however, significantly lower than the expression power of silver films (generally having the resolution of several thousands dpi). The printer accordingly has the problem that dots are visually observable to cause granularity in a resulting printed image. Some techniques have been proposed, in order to solve this problem. The proposed technique provides inks of different densities or applies the mechanism of varying the dot diameter to carry out printing with low-density dots or with small-diametral dots.
In the configuration of printing an image by dots, dots created by a black ink having the highest density causes the highest degree of granularity. The conventionally known technique accordingly does not use the real black ink but expresses a black color (generally referred to as the composite black) with three primary color inks in the case of high-quality printing of an image.
The known composite black technique that expresses the black color with three primary color inks, however, requires dots of all the three primary colors to express a single black dot. This triples the required number of dots. The following problems arise due to an increase in number of dots required for expressing an achromatic color of a specific density:
(1) In an ink jet printer that provides an ink prepared by dissolving a pigment or a dye in a solvent and causes the ink to be ejected as ink droplets on printing paper, the total quantity of inks ejected per unit area is restricted by the ink duty of the printing paper, that is, the quantity of ink that can be absorbed by the printing paper. The total quantity of inks to express the black color by the composite black may exceed the restriction of the ink duty in the event that the printing paper used has a relatively low ink duty.
(2) The composite black technique expresses the black color with three primary color inks. There is accordingly insufficiency of the required density as the black color and may give certain unclearness to the whole image. In the event that the three primary colors have high dot densities, the overlap of the respective color dots created in a certain sequence may cause color mismatch. Especially in the case of non-liquid inks, such as thermally fusible inks, the overlap of the respective dots may give the impression of coating the different inks one after another. It is accordingly difficult to attain the dot density of or over a certain level as the black color.
(3) At the boundary where the dots of the composite black are gradually replaced by the dots of the real black ink, the state filled with the dots of the three different color inks to express the black color is changed to the state filled with the dots of only one black ink to express the black color. The blotting condition may change over the boundary when the printing paper is readily affected by the blot. In this case, the resulting printed image may not have a uniform picture quality.
A variety of techniques have thus been proposed to partly replace dots of the real black ink with dots of the composite black in an allowable range specified by the ink duty and the restriction of the dot density. In any of such known techniques, dots of the real black ink are created at or over a predetermined density. This undesirably worsens the granularity at the boundary that starts creation of dots by the real black ink.
The object of the present invention is thus to adjust hues of at least two different inks and satisfy a predetermined ink duty of a printing medium and other required conditions without lowering the picture quality of a resulting recorded image in a printer with a head that is capable of recording a plurality of different inks on the printing medium.
At least part of the above and the other related objects is attained by a printer with a head that is capable of recording a plurality of different inks on a printing medium. Two among the plurality of different inks are a specific chromatic color ink having a predetermined hue and a particular ink having a certain hue that is mixed with the specific chromatic color ink at a predetermined rate to express a black color. The printer includes a black color recording unit that causes the head to record the specific chromatic color ink and the particular ink at the predetermined rate on the printing medium, so as to express the black color.
The present invention is also directed to a method of printing, which corresponds to the above printer. The method causes a printer to print an image with a head that is capable of recording a plurality of different inks on a printing medium. The method includes the steps of: providing a specific chromatic color ink having a predetermined hue and a particular ink having a certain hue that is mixed with the specific chromatic color ink at a predetermined rate to express a black color, as two among the plurality of different inks; and causing the head to record the two inks at the predetermined rate on the printing medium, so as to express the black color.
The printer or the printing method corresponding thereto of the present invention provides the specific chromatic color ink having a predetermined hue and the particular ink having a certain hue that is mixed with the specific chromatic color ink at a predetermined rate to express a black color, as two among the plurality of different inks used for printing. The head is made to record the specific chromatic color ink and the particular ink at the predetermined rate on the printing medium, so as to express the black color. In order to record an achromatic multi-tone image, black dots are not created solely by real black ink but are created by the specific chromatic color ink and the particular ink that expresses the black color in combination with the specific chromatic color ink. Compared with the case in which black dots are created solely by the real black ink, this arrangement of the present invention enables printing with less granularity.
From the viewpoint of reducing the degree of granularity of dots, it is desirable that both the two inks cause less granularity. It is also preferable to use, as the specific chromatic color ink, a color ink causing low granularity when dots are recorded with the color ink on the printing medium, for example, yellow ink.
The technique of expressing the black color with the two inks is applicable to a printer for multi-color printing. In this case, the printer has an ink cartridge that accommodates therein, as the plurality of different inks, the specific chromatic color ink and the particular ink, as well as another color ink, which corresponds to one of three primary colors and is capable of expressing a predetermined color space in cooperation with the specific chromatic color ink having the predetermined hue. The printer also includes: an ink rate setting unit that sets a rate of quantities of the respective inks corresponding to a color to be expressed in the predetermined color space; and a head driving unit that drives the head to record the respective inks on the printing medium at the rate set by the ink rate setting unit, with regard to image data to be printed.
This printer enables multi-color printing with the three primary colors, and does not express the black color as composite black formed by three different inks. The printer uses one color ink corresponding to one of the three primary colors and another ink that is capable of expressing the black color in combination with the color ink, in order to express the black color. This arrangement does not require three different inks to express the black color, thereby satisfying the restriction by the ink duty of the printing medium and reducing the possibility of color mismatch due to overlap of different color dots. The black color expressed by this arrangement gives a clearer impression to the resulting image than the composite black.
In accordance with one preferable application of the printer having the configuration discussed above, the respective inks are liquid, and the head has a mechanism for causing each of the respective inks to be ejected in the form of ink droplets on the printing medium. A specific value that satisfies an ink duty of the printing medium is set to the rate of the quantities of the respective inks. In the case of liquid ink, it is extremely important to satisfy the ink duty set for each printing medium, that is, the upper limit of ink quantity absorbable by the printing medium. This arrangement of the printer enables the ink duty set for each printing medium to be readily satisfied and gives less granularity to the resulting printed image.
The technique of the present invention expresses the black color by mixture of two different inks. It may be preferable to use a specific ink cartridge to attain such printing. The present invention is thus directed to an ink cartridge attached to a printer with a head that is capable of recording a plurality of different inks on a printing medium. Two among the plurality of different inks are a specific chromatic color ink having a predetermined hue and a particular ink having a certain hue that is mixed with the specific chromatic color ink at a predetermined rate to express a black color. At least one of these two inks is accommodated in the ink cartridge.
This ink cartridge is applicable for the printer that expresses the black color by mixture of two different inks. These two inks are reserved in different ink chambers located in one identical ink cartridge. This arrangement enables at least two required inks to be supplied efficiently from one ink cartridge to the printer.
The specific chromatic color ink included in the ink cartridge may be any one of cyan ink, magenta ink, and yellow ink. Any of these inks can be supplied stably at relatively low cost.
It is also preferable that the ink cartridge accommodates another color ink that corresponds to one of three primary colors and is capable of expressing a predetermined color space in cooperation with the specific chromatic color ink having the predetermined hue, in addition to the two inks. In this case, the specific chromatic color ink is commonly included in both the two inks for expressing the black color and at least three color inks for expressing the predetermined color space. This ensures the desirable size reduction of the ink cartridge.
In accordance with one preferable application, a volume of the common specific chromatic color ink accommodated in the ink cartridge is preset to be greater than a volume of the another color ink by a predetermined factor. This arrangement effectively prevents the unbalance quantities of the inks from remaining in the ink cartridge.
The technique of the present invention may be attained by the computer and provided as a program product in which a program code is recorded in a recording medium. The present invention is thus to directed to a program product that includes a program code, which causes a printer to print an image with a head that is capable of recording a plurality of different inks on a printing medium, and a recording medium in which the program code is stored in a computer readable manner. The program code includes: a first program code that causes a computer to input a density of black color included in an image to be recorded; a table that stores recording rates of a specific chromatic color ink and a mixing black ink, which are included in the plurality of different inks, corresponding to a varying density of black color, the specific chromatic color ink having a predetermined hue, the mixing black ink having a certain hue that is mixed with the specific chromatic color ink at a predetermined rate to express a black color; and a second program code that causes the computer to refer to the table and determine the recording rates of the specific chromatic color ink and the mixing black ink corresponding to the input density of black color.
A computer incorporated in a printer, or alternatively a printer driver of a computer in the case where the computer is combined with a printer to constitute a printing system, reads the program product to attain the functions discussed below. The printer provides a specific chromatic color ink having a predetermined hue and a particular ink having a certain hue that is mixed with the specific chromatic color ink at a predetermined rate to express a black color, as two among the plurality of different inks used for printing. When reading the respective program codes included in the program product, the printer causes the head to record the specific chromatic color ink and the particular ink at the predetermined rate on the printing medium, so as to express the black color. In order to record an achromatic multi-tone image, black dots are not created solely by real black ink but are created by the specific chromatic color ink and the particular ink that expresses the black color in combination with the specific chromatic color ink. Compared with the case in which black dots are created solely by the real black ink, this arrangement of the present invention enables printing with less granularity.
The program product may also include other elements to attain the functions corresponding to the various applications of the printer discussed above. By way of example, the program code of the program product may further include: a third program code that causes the computer to identify an ink cartridge attached to the printer and determine which of an ink cartridge accommodating therein the mixing black ink and another ink cartridge accommodating therein a real black ink that is capable of expressing a black color independently; a fourth program code that causes the computer to select an appropriate table for the identified ink cartridge among a plurality of tables, which are provided for different ink cartridges and store recording rates of respective inks corresponding to a varying density of black color; and a fifth program code that causes the computer to refer to the selected table and determine the recording rates of the respective inks.
The printer reading these program codes identifies the ink cartridge attached to the printer and refers to the appropriate table corresponding to the identified ink cartridge for printing.
In accordance with another embodiment, the program code of the program product may further include: a sixth program code that causes the computer to identify an image to be recorded; a seventh program code that causes the computer to record an image with an ink cartridge accommodating therein the mixing black ink in the case where the identified image is a natural picture; and an eighth program code that causes the computer to record an image with another ink cartridge accommodating therein a real black ink that is capable of expressing a black color independently, in the case where the identified image is not a natural picture.
Another application of the present invention is a product that includes data, which are referred to by a program for controlling a printer that prints an image with a head that is capable of recording a plurality of different inks on a printing medium, and a recording medium, in which the data are recorded in a computer readable manner. The data include a table that stores recording rates of a specific chromatic color ink and a mixing black ink, which are included in the plurality of different inks, corresponding to a varying density of black color included in an image to be recorded. The specific chromatic color ink has a predetermined hue, and the mixing black ink has a certain hue that is mixed with the specific chromatic color ink at a predetermined rate to express a black color.
The computer incorporated in the printer reads the program codes or data discussed above to actualize the specific functions of the printer. The characteristics of the program codes or data may be known without causing the printer to perform the related operations but by analyzing the program codes or data recorded in the recording. The program codes or data are generally recorded in a recording medium, such as a CD-ROM or a flexible disk, but may alternatively be stored in a storage medium, such as a hard disk in the computer, or transmitted in the form of a protocol or a carrier wave through a computer network. A plurality of program codes constituting one program product may be recorded separately in different recording media. In accordance with another possible application, a program code relating to the basic operations of a printer is incorporated in advance in the printer, whereas a program code corresponding to the principle of the present invention may be distributed separately. These configurations also correspond to the program product of the present invention. By way of example, when the ink cartridge attached to the printer accommodates at least one of the specific chromatic color ink having a predetermined hue and the particular ink having a certain hue that is mixed with the specific chromatic color ink at a predetermined rate to express a black color, a specific program code that actualizes the printing method discussed above by taking advantage of the properties of the inks accommodated in the ink cartridge may be attached to the ink cartridge, for example, in the form of a flexible disk. The specific program code may alternatively be transmitted from a web page through a computer network such as the Internet.